In the 2002 film Like Mike, a teenage orphan by the name of Calvin Cambridge finds an old pair of basketball shoes with the faded initials "M.J." written on the inside, and convinces himself that they once belonged to Michael Jordan. He soon finds out that the shoes are contagious, imparting those who wear them with extraordinary prowess on the basketball court, and then goes on to enjoy a successful career as a professional player.

The superstitious belief that using a professional's equipment will improve one's own performance is very popular among amateur athletes. This particular belief may be more than just a superstition, however. According to a new study in the open access journal PLoS ONE, amateur golfers who believed they were using a professional golfer's putter not only sunk more putts than others, but also perceived the hole to be bigger.The law of contagion is a form of magical thinking that was first described more than a hundred years ago by James George Frazier. "Things which have once been in contact with each other continue to act on each other at a distance after the physical contact has been severed," he wrote in his classic 1890 book The Golden Bough: A Study in Magic and Religion. "[The magician] infers that whatever he does to a material object will affect equally the person with whom the object was once in contact, whether it formed part of his body or not."

The law thus describes the belief that brief contact with an object can lead to the permanent transfer of certain properties to another object. In the case of sporting equipment, contagion is believed to have positive effects, but it can have negative ones, too. For example, one study published in 1986 showed that drinks which had come into brief contact with a sterilized dead cockroach, and clean clothes believed to have been previously worn by an unpopular person, were both rated as being undesirable.

For the new study, Charles Lee and his colleagues at the University of Virginia's Perception Lab recruited 41 undergraduates, all of whom indicated having previous golf experience and enthusiasm for the sport. The participants were randomly split into two groups and the researchers told those in one group that they had obtained a putter once used by the professional golfer Ben Curtis.

All of the participants were then shown a putting matt. They were first asked to estimate the size of the golf hole on the matt, using the elliptical tool in Microsoft Paint, and then used the same putter to take 10 putts on the matt. Those who believed they were using the professional golfer's putter consistently perceived the golf hole to be larger than those in the other group. Furthermore, the belief improved their performance – they also sank more putts than the others.

Several years ago, psychologist Jessica Witt of Purdue University and her colleagues reported that sporting performance affects the perception of goal size. Participants were asked to perform field goals on a practice American football field and then to estimate the size of the goal. Those who scored three or more goals perceived the goal to be bigger than those who scored two or less, suggesting that some kind of feedback mechanism modulates perception according to performance.

The new study extends this earlier work, and shows that the relationship between action and perception is more complex than previously thought. It shows that changes in the apparent size of the golf hole can occur before any putting has taken place. Thus, feedback on one's performance is apparently not necessary for such perceptual changes, and it may be the case that the observed increases in the apparent size of the golf hole led to improved performance.

The authors provide several explanations for how positive contagion influenced putting performance. The belief of some participants that they were using Curtis's putter may have encouraged them to use positive mental imagery associated with his past successes. Another possibility is what is referred to as priming: believing the putter was once used by a professional could have led the participants to entertain the concept of "skill".

Finally, the results could be explained by object valuation, which can have a powerful placebo effect. For example, the price of medication impacts on its efficacy, with more expensive medications being more efficacious than cheaper ones. By the same token, expensive wines are perceived to taste better than cheaper ones. Thus, the belief that one is using a professional's putter could enhance one's own perceived putting capabilities in a similar way. Although such effects are difficult to measure experimentally, this new study lays the groundwork for further research into the possible scientific basis of other superstitious beliefs.